This invention relates generally to gas turbine engines, and more particularly to fan blades of a gas turbine engine.
A turbofan gas turbine engine used for powering an aircraft in flight typically includes, in serial flow communication, a fan assembly, a low pressure compressor or “booster”, a high pressure compressor, a combustor, a high pressure turbine, and a low pressure turbine. The combustor generates combustion gases that are channeled in succession to the high pressure turbine where they are expanded to drive the high pressure turbine, and then to the low pressure turbine where they are further expanded to drive the low pressure turbine. The high pressure turbine is drivingly connected to the high pressure compressor via a first rotor shaft, and the low pressure turbine is drivingly connected to both the fan assembly and the booster via a second rotor shaft.
The fan assembly includes a plurality of circumferentially spaced apart fan blades extending radially outwardly from a rotor disk or hub. The fan blades generally comprise an airfoil and an integral dovetail at the airfoil root. The dovetail is received in a complimentary dovetail slot formed in the rotor disk. Fan blades are typically made of either a metal, such as titanium, or a composite material, such as a carbon-epoxy composite system. A radially inner flowpath boundary for the airflow channeled between the blades is provided by an array of fan platforms located between adjacent fan blades, near the rotor disk.
It is desirable for the fan to have the smallest possible radius ratio, i.e., the radius of the hub to the radius of the blade tips, because minimizing radius ratio maximizes fan inlet area and allows the greatest possible thrust for a given fan diameter.
The radius ratio may be lowered by reducing the hub diameter and placing the platforms as far radially inboard as possible. However, some fan blade designs incorporate a straight axial dovetail, requiring a large radial transition area between cambered airfoil and straight dovetail. This design also does not allow for disk to form part of the platform.
Accordingly, there is a need for a fan blade structure incorporating a straight axial dovetail which is compatible with an inboard position of adjacent platforms.